This invention relates to a magnetic recording medium, and more specifically to a high-density magnetic recording medium.
Magnetic recording media as magnetic tapes, disks and the like are in wide use for audio and video recording-reproducing units and for computers. In these fields, intensive researches are being pursued for the development of higher density media. As is well known, the magnetic recording system basically performs recording and reproduction of signals with a magnetic head. Therefore, realization of a higher density medium calls for some means to minimize the loss between the medium and the head in addition to the means for improving the magnetic properties of the medium and achieving uniform distribution of magnetic particles in the magnetic layer of the medium. Efforts have been exerted, for instance, to make the magnetic layer surface as smooth as possible and thereby lessen the tape-head separation loss. Improvements in contact between the head and the medium with smoother mirror finish have, however, been attained at some sacrifice of the strength of the magnetic layer. This has been found to pose new problems of the magnetic coating coming off upon contact with the head, deposition of the magnetic powder on the head, and eventual head clogging. As a solution to these and other problems it has been practiced to add a small amount of abrasive particles having an average particle diameter of about one micron to the magnetic coating. The particles usually used as the abrasive are those of Al.sub.2 O.sub.3, Cr.sub.2 O.sub.3, SiC, .alpha.Fe.sub.2 O.sub.3 and the like. They are added as sparsely as feasible to the surface portion of the magnetic layer to avoid deterioration of the electromagnetic conversion characteristics and minimize the wear of the head. With the common practice, however, it has been found that the pursuit of higher density for the magnetic recording medium, through the addition of finer magnetic powder, increase in coercive force, and smoothening of the magnetic coating surface, is accompanied with drawbacks of inadequate tape strength and inability of maintaining the head in an optimum condition with respect to the higher density medium.
The present invention is based on a thorough review of the role the abrasive plays and consequent discovery of conditions essential for the manufacture of a higher density recording medium.